1. Field of the Invention
The present invention relates to a methanol oxidation catalyst and a method for manufacturing the methanol oxidation catalyst.
2. Description of the Related Art
Solid polymer type fuel cells, and particularly those using an aqueous methanol solution fuel, convert chemical energy into electric power by the catalytic reaction of an electrode. Therefore, a highly active catalyst is essential to develop high-performance fuel cells. As is known the catalyst typically comprises a combination of platinum (Pt) and ruthenium (Ru).
The theoretical voltage obtained by the catalytic reaction of the electrode is 1.21V, whereas the voltage loss due to the PtRu catalyst is about 0.3V. Therefore, an anode catalyst having a higher activity (methanol oxidation activity) than that of PtRu is desired. Current PtRu anode catalysts have problems due to dissolution (elution) of Ru, and therefore, highly active methanol oxidation catalysts having a Ru-free composition are desired.
To date, studies have been made as to methanol oxidation catalysts having various composition types. For example, a method in which metals such as tungsten, tantalum and niobium are added to a PtRu catalyst is described in U.S. Pat. No. 3,506,494. Japanese Patent Applications, publication Numbers 2004-281177 (KOKAI) and 2006-179445(KOKAI), describe a sputtering process for manufacturing a catalyst. There are only a few reports as to a reduction in the amount of Ru to be added and Ru-free compositions.
In the case where the catalysts are nanoparticles, the surface electron state of the catalyst particles and the nano-structure of the particles are strongly dependent on the catalyst composition and in particular type and amount of elements. In order to obtain high activity and high stability, the type and amount of the elements and combination of the elements need to be appropriately selected. To date, studies concerning catalyst compositions and synthesis processes are insufficient and a highly stable catalyst having sufficient methanol oxidation activity has not been established.